The mission of the Genetic Mouse Models Shared Resource is to provide a centralized resource to the members of the San Antonio Cancer Institute for the design, generation and evaluation of genetically altered mice. The shared resource is Directed by Paul Hasty, D.V.M., who has extensive experience in the production and analysis of knockout mice and in the use of knockout mice in cancer research. He has generated and analyzed mice mutated for many genes including the DNA repair genes Rad51, Ku80 and Brca2. In addition, Dr. Hasty was the Director at Lexicon Genetics, Inc., in charge of the mouse knockout unit (Lexicon Genetics generates several hundred knockout mice per year). The Genetic Mouse Models Shared Resource will be essential to meet the developing scientific needs of of SACI memebrs in both basic and translational research. Services include: 1. Design of genomic alteration: Assistance is provided in protocol design from basic knockouts to a wide-range of more sophisticated approaches such as tissue-specific and conditional knockouts. In addition, this Core will provide transgenic services using mouse embryonic stem (ES) cells. 2. Isolation of ES cells with the desired genomic alteration: DNA vectors are transfected into ES cells and the appropriate selection media is applied. Drug-resistant colonies will be isolated, expanded and replica-plated. 3. Generation of genetically altered mice (heterozygotes): ES cells with the appropriate genetic modification will be injected into donor blastocysts and transferred into pseudopregnant females. These chimeric mice will be bred to obtain genetically modified heterozygote mice. After genotyping the chimera's progeny, the genetically modified mice will be delivered to the investigator. 4. Consultation on analysis of genetically altered mice: Once the genetically altered mice have been established, the Genetic Mouse Models Shared Resource will consult with investigators on husbandry, genotyping and phenotypic analysis.